Screw rolling die



c. c. RICHARDS 2,336,190 SCREW ROLLING DIE Filed Augf30, 194C INVENTOR 28 Charles 6. Rdafiarais ATTORNEYS Patented Dec. 7, 1943 UNITED STATESPATENT OFFICE SCREW ROLLING DIE Cecil Charles Richards, West New York, N. J., assignor to Groov-Pin Corporation, Union City, N. J., a corporation of New York Application August 30, 1940, Serial No. 354,823

3 Claims.

.The substantial amount of metal displaced and scooped out in rolling the relatively deep and wide grooves that traverse the entering ends of the threads of such screws generally collects along the ends of the thread segments at the lateral walls of the grooves with resultant dulling, rounding and substantial elimination of those edges upon the sharpness of which the cutting or tapping effectiveness of that type of screw depends. Moreover the presence of such excess displaced metal frequently results in misshapen thread segments at the grooved regions. Relatively great effort is therefore required to apply the resultant screw, for it obviously tends to gouge rather than to cut the metal of the bore into which it is to be'screwed; its retaining power is accordingly deficient and it is unsatisfactory and unmarketable for many of the most important applications for which that type of screw should be ideally adapted.

Among the objects of the invention are to provide apparatus by which may be expeditiously rolled uniform and effective self-tapping screws" of the above type, characterized by accurate formation of the threads and sharpness and toughness of the cutting or tapping edges of the interrupted thread segments of the screw.

Another object is to provide a die construction for the above purpose, involving the use of die plates of length that need be no greater than the minimum length required for thread rolling and characterized by simplicity, durability and low cost, which may be set up with facility for rolling the screens and without the need for superlative precision and therefore without the need for continued examination and frequent adjustments thereof.

The invention involves the downward sloping or bevelling off of the thread rolling die near its outlet end, desirably into a broad gently beveled incline to a depth no greater than the depth of :thread to be rolled. The thread formingribs of uniform height extend parallel to the respective horizontal main area of die plate and the downwardly sloping bevel area thereof. By this simple modification in the otherwise conventional rolling die plate, marked improvement in the rolled product is attained. The metal which collects as a welt at the edges of the thread segments between the grooves as these are rolled into the thread forming blank is eliminated by that part of the rolling operation which occurs at the bevel area of the thread rolling die. This is due to the fact that as the screw is rolled along said beveled area the groove rolling ribs on the companion plate have progressively reduced displacement and scooping effectiveness upon the substantially completely rolled grooves with which said ribs mesh. Accordingly, the welts at the cutting edge of the thread segments due to the accumulation of metal thereat displaced in rolling the grooves, are progressively diminished and finally eliminated by the continued effective thread rolling and smoothing operation at the beveled area of the thread rolling die.

In the present application the screw rolling die alone is claimed. The method of making such die, the screw produced thereby and the method of rolling the same are the subject matter of my divisional application Serial No. 495,843 filed July 23, 1943.

In the accompanying drawing in which is shown one of various possible embodiments of the several features of the invention,

Fig. 1 is a diagrammatic view, indicating one step in making the thread rolling die plate according to the invention,

Fig. 2 illustrates diagrammatically the step of machining the thread rolling ribs into the main die plate area,

Fig. 3 shows a view similar to Fig. 2 illustrating the machining of the thread rolling ribs in the beveled end portion of said plate,

Fig. 4 is a perspective view showing the general relationship of the coasting dies for rolling the thread,

Fig.5 is a fragmentary perspective view on an enlarged scale showing the conformation of the screw at one stage of the operation,

Fig. 6 is a view similar to Fig. 5 showing the conformation of the completely rolled screw,

Fig. 7 is a view in transverse cross-section showing the operation in the final or clean-up stage of thread rolling, and

Fig. 8 is a side elevation of the completely rolled screw.

Referring now to the drawing, there is shown in Figs..l, 2 and 3, a desirable method of preparthe die plate of the complementary plate. ribs are desirably of height ing the thread rolling die plate used in the combination and in carrying out the method of thread rolling, and which die plate itself constitutes one aspect of the invention. The blank plate I ii is first clamped in the vice diagrammatically indicated at H and adjusted at a slight inclination by appropriately positioning the swivel base IE on the milling machine which mounts the said vice. Thereupon the upwardly sloping end of the plate is machined off to a bevel l3 as shown in Fig. 1. Desirably the extreme edge of j grooving operation by the groove rolling ribs 2|.

the bevel thus formed is disposed below the main face M of the die plate by a distance no greater and ordinarily equal to the depth of thread to be rolled. In most embodiments, the width of the shallow bevel thus formed, would be approximately 35 per cent of the total length of the die plate.

The die plate is thereupon adjusted to horizontal positionas shown in Fig. 2 and. at the desired thread pitch angle, and the thread rolling ribs I5 are machined thereon until the cutters l 6 run out of the bevel portion I3 as for instance at It.

Thereupon as shown in Fig. 3, the die plate is again adjusted upon the base of the milling machine to the position shown in Fig. 1, in which ,the face of the bevel l3 extends horizontally and the milling cutters l 6 continue the cutting of the thread forming ribs as at I! throughout the beveled areaof the plate. The thread rolling ribs thus protrude a uniform distance aboveth'e main area 14 and the beveled area l3 respectively of l0. Theresultant obtuse points l3 between rib segments l5 and I1 of the thread rolling ribs on the main and beveled areas respectively of the plate may then, if desired, be rounded off at IS. The plate is thereupon h'ardened according to familiar practice.

If desired the order of machining the thread rolling rib segments as shown in Figs. 2 and 3 may of course be reversed. a

The companion die plate in a preferred embodiment is shown at the top of Fig. 4. From one longitudinal edge thereof and for a substantial I portion of the width thereof, the latter plate has groove rolling ribs 2| extending transversely thereof at desired steep angle with respect to the thread'rolling ribs 22 that correspond to those of the plate I0 and extend along the rest The groove rolling greater than the thread rolling ribs l5, so that in the finished screw product as shown-in Fig. 8 grooves 23 that interruptthe threads at the tapping end of the screw, extend inward below the root diameter 24 of the threads.

The main areas of the two plates Ill and 20 are maintained in parallel relation in the'process of rolling the threads upon suitable pieces of stock (not shown), desirably tapered at theen-' try end thereof. In the rolling of such blanks between the main areas of the complementary die plates, the threads and grooves are simultanecusly formed. As shown in Fig. 5, a substantial amount of metal: is displaced and scooped out. of the blank'sto'ck by the rotation of said blank part past successive groove rolling ribs 2 l,

which'tends to pile up, particularly at the leading edge of the groove as a welt shown at 26 and to a degree also at the trailing edge thereof.

If ordinary dies were used without the beveled conformation above described, the sudden release of pressure upon the deformed shank as it .not displaced or distorted. .according to the present invention, will tap its 'ed to a progressively reduced displacement and By reason of the progressively increasing distance between the plates ID and 20, the grooves 23 in the rolled blank mesh with the groove rolling ribs 2| as best shown in Fig. 7, with progressively lessened displacement and scooping action of the latter, and near the end of the die the displacement and scooping action ceases. However,

the pressure of the groove rolling plate 20 upon the screw being formed remains sufiicient to continue the effective rolling of the thread segments 2'! between consecutive grooves 23.

Accordingly, the welts 26 become flattened, spread and worked into the surface areas of the thread segments. In other words, as the effectiveness of the groove rolling is progressively reduced in the final stretch of the rolling operation, the thread rolling action is maintained with adequate effectiveness to elfect the smoothing operation set forth.

It will moreover be seen that in the course of its progress along the bevel area l3, the screw blank being formed is permitted gradually to return from its compressed. generally elliptical cross-section to the generally circular cross-section shown in Fig. 7, and the deformation of screw incurred by sudden release of pressure is obviated.

The self-tapping screw is thus completely 'formed without further machining operation, in

a single thread rolling operation and the cutting edges 28 at the sides of the respective grooves 23 are sharp and at the required steep cutting angle. Also the thread segments 21 intervening between the grooves are accurately formed and The screw rolled way into the bore with substantially the efiectiveness of a tapping tool, to cut a clean, well-formed thread with a minimum of efiort and without tearing or gouging the metal or deformation thereof. The consequence is not only that the screw is more readily applied, but that the main shank thereof fits the tapped bore with considerably enhanced security.

Moreover, the final stage of the thread rolling operation along the beveled area I 3 of the die plate It results in compressing the excess protruding metal that forms the objectionable welts 26 into the thread segments, particularly at the neighborhood of the tapping edges and therefore tends to toughen and'harden the metal at said edges with advantageous improvement in the wearing qualities and cutting effectiveness 7 at the parts that perform the tapping when the screw is applied.

While the novel die plate I0 is preferably made by the method described, as shown in Figs.:1 to 3, it is of course understood that the dieplate' per se might be prepared, within the scope of certain of the claims, by other methods that'will readily suggest themselves to those skilled in the art.

Where it is attempted to roll screws by straight die plates held at slightly diverging angle, the maximum effectiveness of rolling may be lost early in the operation, and longer and more costly dies and correspondingly slower production results, aside from the fact that the adjustment of said die plates is a difilcult operation which requires great precision, and the advantageous degree of toughening of the metal at the tapping or cutting edges of the screw does not occur.

As many changes could be made in the above method and products and many apparently widely difierent embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having thus describing my invention, what I claim as new and desire to secure by Letters Patent is:

1. A thread rolling die having the thread rolling ribs extending obliquely in parallel relation from one end to the other thereof, the face of said die at the exit portion thereof extending in a plane sloping slightly from the horizontal or main area of the die, the thread rolling ribs extending to a uniform height respectively from the main area of the die and from the sloping end area thereof.

2. A thread rolling die plate with thread rolling ribs extending obliquely in parallel relation from one end to the other thereof, the face of said plate at the exit portion thereof extending in a plane sloping downward slightly from the horizontal or main area of the plate, the thread rolling ribs extending to a uniform height from the main area of the die and from the sloping end area thereof, the obtuse angle between the main lengths of ribs and those of the sloping end of the die being rounded off.

3. A screw rolling die assemblage comprising a pair of coacting plates, said pair of plates including one plate with thread rolling ribs and a companion plate with groove rolling ribs of height greater than the thread rolling ribs and trav-, ersing only a portion of the width of the thread 20 rolling plate, the thread rolling plate near the discharge end thereof having a shallow bevel to a depth no greater than that of the thread to be rolled, the thread rolling rib segments protruding to uniform height along the bevel, equal 25 to that of the corresponding rib segments along the main area of plate.

CECIL CHARLES RICHARDS. 

